. 2022 Jan 14;34(5):1113–1121. doi: 10.1007/s40520-021-02033-4
© The Author(s), under exclusive licence to Springer Nature Switzerland AG 2021
This article is made available via the PMC Open Access Subset for unrestricted research re-use and secondary analysis in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.
Fig. 1.
Flow diagram of the study design